At present, backlight modules in liquid crystal display devices mainly include two types of edge-type and direct-type, and generally, an LED (Light Emitting Diode) is used as a light source in the backlight module. The edge-type backlight module generally adopts a light guide plate while the direct-type backlight module generally adopts a diffuser plate, so that the light emitted from the light source forms a uniform surface light source. In order to reduce cost, the direct-type backlight module adopting the diffuser plate gradually replaces the edge-type backlight module adopting the light guide plate which is relatively expensive, and is widely applied in low cost products.
In the direct-type backlight module, LEDs are usually arranged on a backplane at a certain interval therebetween. In order to reduce the cost and obtain a light-exiting surface from which light is emitted uniformly, LEDs are mainly arranged in the following two manners: one manner is to arrange a large number of low power LEDs densely on a backplane, but, since the number of the LEDs is large (generally several hundred), problems of color difference and poor reliability occur; the other manner is to arrange several, even dozens of, high power LEDs on a backplane along with a secondary optical lens, in which emergence angle of the LED can be increased and the number of LEDs can be reduced, but, since the high power LED has a large volume chip and the light emitted therefrom has a high intensity, a problem of severe lamp shadow occurs, which cannot be improved even after light conversion by the secondary optical lens, in addition, as the light having high intensity needs a longer distance for light mixing, so that the whole backlight module has a large thickness.